A New Metallographic Technique for Revealing Grain Boundaries in Aluminum Alloys

Abstract

A new metallographic technique has been developed for revealing the grain structure of common 5000 and 2000-series aluminum alloys. Grain structures of these aluminum alloys are normally difficult to reveal with common etchants. The preferred metallographic etchant for structural aluminum alloys is generally based on HCl, HNO3, and HF, usually referred to as Keller's reagent. At times, however, this etchant does not give completely satisfactory results. This is true when the structure is inhomogeneous, having patches of recrystallized and non-recrystallized grains, or clusters of intermetallic particles in material containing few particles. Samples with a poor final polish and a smeared surface also do not respond well to Keller's etchant. The new technique described in this article consists of two steps: 1. a pre etchant with a solution of 1 g NaCl in 50 ml H3PO4 (40%) and 2. etch with Weck's reagent. The microstructures obtained with this new method are compared with Keller's and Weck's reagents. © 2012 Springer Science+Business Media New York and ASM International.